Looks like black beard algae (also called black brush algae). It's a real pain...I had it in a tank once and couldn't get rid of it no matter what I did. Hopefully someone else will have some suggestions.

Yes! I have that too (yes it is BBA), but with the right stuff, it is easy to kill. Get yourself a 1ml syringe from a chemist and a bottle of Seachem's Flourish Excel. Fill the syringe with Excel and use it to spot-treat the algae-covered bits. Leave your filter off for one hour after the treatment. Do it daily. The algae should start to turn red, then die. It won't harm your plants or any critters in the tank. :)

Did this method work? I have a terrible outbreak of black brush algae and have been adding Flourish excel to the water as a supplement for my java fern daily but it never solved my problem. I have not attempted to "spot clean" the ferns as there is so much :( But I will do so if it works! I really want to save the plants and not toss them...